1. Field of the Invention
The present invention relates to a graphite sheet or block material suitable to a dopant interphase intercalation, which is used for a secondary battery, a circuit substrate, a shield material and so on, especially a graphite sheet or block used for the secondary battery wherein an active material can be intercalated between graphite phases or layers.
2. Prior Art
Many kinds of graphite have been proposed for an anode material of a lithium secondary battery as shown in U.S. Pat. No. 4,980,250 (inventors: Takahashi et al.), No.5,069,683 (inventors:Fong et al.), No. 5,153,082 (inventors: Ogino et al.), No. 5,244,757 (inventors: Takami et al.). In all cases, however, the anode material is made of carbon or graphite powder and/or fibers and binders, so that the electric conductivity is not good in comparison with the carbon or graphite material itself.
On the other hand, as reported by Japanese Patent Kokai 4-79155, a graphite sheet or block can be prepared directly from a specific polymer film by graphitizing at a high temperature. The graphite sheet has a good electric conductivity since graphite crystalline orientation is arranged along the sheet surface. However, the graphite sheet has a disadvantage that it is difficult for an active material or dopant to be intercalated from the sheet surface into the graphite interphase because of such a graphite crystalline orientation, so that the graphite material can not show the good characteristics of battery charge-discharge if used in the anode of the lithium secondary battery.